Monetizing via the Apple App Store - Beginning iOS6 Games Development - page 245

In Listing 10-3, we see the task productsRequest:didReceiveResponse: that gets called when we
have a valid set of product IDs. In this task, we simply iterate over all of the products returned and
make our buttons visible for purchasing saucers and power-ups. In this way, we make sure the user
only sees viable purchase options.
We also map each of valid product IDs to the SKProduct objects set to the application. In this way,
when the user makes a purchase, we can pull out the exact object Apple sent to us. This ensures we
are presenting good data to our users.
We have looked at how we figure out which purchases are valid. Before we look at how purchases
are actually made, we should examine the class GameParameters . The class GameParameters is
responsible for storing which products have already been purchased and which actors the user
wants in his or her game.
Driving the UI from Existing Purchases
The three buttons, shown in Figure 10-1 , allow the user to select which actors are available in the
game. The same UI allows the user to purchase new actors. In order to keep track of this information
we have created the model class GameParameters , whose header is shown in Listing 10-4.
Listing 10-4. GameParameters.h
@interface GameParameters : NSObject<NSCoding>
@property (nonatomic) BOOL includeAsteroids;
@property (nonatomic) BOOL includeSaucers;
@property (nonatomic) BOOL includePowerups;
@property (nonatomic, retain) NSMutableSet* purchases;
+(id)gameParameters;
+(id)readFromDefaults;
-(void)writeToDefaults;
@end
In Listing 10-4, we see the header for the class GameParameters . We have three BOOL properties
to keep track of which actors the user wants in the game. We also have an NSMutableSet called
purchases that is used to store a set of product ID strings. The constructor gameParameters will
create a new GameParameters object with no purchases and only includeAsteroids set to true
(implementation not shown). The class task readFromDefaults is used to pull a GameParameter out of
the default NSUserDefaults , whereas writeToDefaults is used to serialize a GameParameter back to
the default NSUserDefautls . Listing 10-5 shows both readFromDefaults and writeToDeafaults .
Listing 10-5. GameParameters.m (readFromDefaults and writeToDefaults)
+(id)readFromDefaults{
NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
NSData* data = [defaults objectForKey:GAME_PARAM_KEY];
if (data == nil){
GameParameters* params = [GameParameters gameParameters];
[params writeToDefaults];